Exposure control for photographic apparatus



United States Patent EXPOSURE CONTROL FOR PHOTOGRAPHIC APPARATUS 10Claims, 2 Drawing Figs.

US. Cl 95/64, 95/10; 352/141 Int. Cl G03b 7/08, G03b 19/18 Field ofSearch 95/ 10C, 64,

Primary Examiner-John M. Horan Assistant Examiner-Joseph F. Peters, Jr.Attorney-Michael S. Striker ABSTRACT: An exposure control forphotographic cameras wherein the armatures of two moving ironinstruments are mounted on a common shaft which carries a diaphragmblade. A control switch is actuated by the shutter release trigger tofirst connect the winding of one instrument in circuit with an energysource whereby the corresponding armature moves the blade to a startingposition. On further actuation of the trigger, the control switchconnects the winding of the other instrument in circuit with the energysource and with a photosensitive resistor so that the position of theblade is changed and the blade defines an aperture whose size is afunction of scene brightness.

PATENTEDUECISIQYC I 354 022 INVENTOR.

RU DOLF BARON KURT THATE EXPOSURE CONTROL FOR PHOTOGRAPIIIC APPARATUSBACKGROUND OF THE INVENTION The present invention relates toimprovements in exposure controls for photographic apparatus. Moreparticularly, the invention relates to improvements in exposure controlsof the type wherein the size of the aperture defined by the blade'orblades of a diaphragm is a function of scene brightness.

It is already known to adjust a multibladediaphra'gm in dependency onthe intensity of scene light. In certain types of such conventionalexposure controls, an armature moves the blade or blades in dependencyon the strength of currents flowing through a winding, and the strengthof such currents is a function of scene brightness because the windingis in circuit with a photoelectric receiver, e.g., with a photosensitiveresistor. The ends of blades carry permanent magnets which cooperatewith the roof-shaped core of an electromagnet. The winding of theelectromagnet is connected in parallel with a photosensitive resistorand the first mentioned winding is in circuit with a battery. If thevoltage of the battery drops after extended use, the magnitude of forceswhich act on the blades as a function of scene brightness decreases;however, the restoring force of the electromagnet which is installedbetween the permanent magnets also decreases to thus compensate for thedrop in battery potential and to prevent inaccuracies in adjustment ofthe diaphragm.

A drawback of the just described conventional exposure control is thatit is prone to malfunction and that it is quite complicated and henceexpensive. The permanent magnets contribute significantly to the initialcost, especially because they must be shaped with a high degree ofprecision. Moreover, care must be taken during assembly to preventcontamination of permanent magnets with ferromagnetic particles of dustor other foreign matter.

SUMMARY OF THE INVENTION An object of the present invention is toprovide a rugged, simple and relatively inexpensive exposure controlwhich exhibits all important advantages of the aforedescribedconventional exposure control.

Another object of the invention is to provide a novel electric circuitryfor the exposure control and to provide the exposure control with anovel instrument which effects displacements of one or more diaphragmblades to optimum positions for making exposures under variouscircumstances.

A further object of the invention is to provide an exposure controlwhich can be incorporated in still cameras or in motion picture camerasand which is also suited for use in single lens reflex cameras.

The improved exposure control comprises diaphragm blade means, rotarycarrier means operatively connected with the blade means to move thelatter between a'plurality of positions including a starting positionand to thus furnish a range of aperture sizes, a pair of moving ironinstruments each including core means, winding means and armature meanswith the armature means of both instruments affixed to the carriermeans, a first electric circuit including one of the winding means, asecond electric circuit including the other winding means and aphotosensitive receiver which is exposed to scene light, and controlmeans movable between a first position in which it completes the firstcircuit whereby the corresponding armature means moves the blade meansto starting position, and a second position to thereby complete thesecond circuit whereby the corresponding armature means moves the blademeans to a position in which the aperture size is a function of scenebrightness.

The exposure contro'l further comprises a source of electrical energy,preferably a single source which is connected in the first and secondcircuits in the first and second positions of the control means. Suchcontrol means may comprise an electric switch which is actuatableby theshutter release trigger.

LII

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved exposure control itself, however, both as to its constructionand its mode of operation, together with additional features andadvantages thereof, will be best understood upon perusal of thefollowing detailed description of a specific embodiment with referenceto the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an exploded perspective andpartly diagrammatic view of an exposure control which embodies theinvention; and

FIG. 2 is a similar exploded perspective view of a detail in theexposure control of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 illustrates an exposurecontrol which comprises a composite moving iron instrument 1 whichincludes two identical instruments numbered 2 and 3. The instrument 2comprises a core 4, a winding 5 and a turnable armature 6; theinstrument 3 comprises a core 7, a winding 8 and a turnable armature 9.The armatures 6 and 9 are affixed to a common rotary carrier 10 hereshown as a shaft having smaller-diameter end portions 11 and 12 whichare received in bores l3, 14 respectively provided in supportingbrackets 15 and 16. A screw 17 connects the lower end portions of theinstruments 2 and 3, and two additional screws l8, 19 are provided tofix the brackets 15, 16 to each other. The screws 18, 19 extend throughopenings provided in the cores 4 and 7. Distancing members 22, 23, 24are interposed between the cores 4 and 7. The shaft 10 is connected witha diaphragm blade 40 having a substantially horn-shaped recess 41. Theblade 40 cooperates with a fixed blade 43 which is installed in frontand overlies a portion of the objective 42. The blades 40, 43 can definea range of aperture sizes in that the blade 40 can move with the shaft10 between a plurality of angular positions including a startingposition or end position which corresponds to an aperture of maximumsize.

The exposure control further comprises two electric circuits one ofwhich includes the winding 5 of the moving iron instrument 2, a variableresistor 26 and a first contact 30a forming part of a control switch 30.The other electric circuit comprises the winding 8, a photosensitivereceiver 27 which is exposed to scene light, a second variable resistor28 and a second contact 30b of the control switch 30. The two circuitscomprise a common source 25 of electrical energy. The control switch 30comprises a third contact 300 which can connect the energy source 25 incircuit with an electric motor 29; the latter is used to operate thefilm transporting mechanism. For example, and if the exposure control ofFIG. 1 is embodied in a motion picture camera, the motor 29 can drivethe customary claw pulldown, not shown. The control switch 30 isactuated by the shutter release trigger 50.

THE OPERATION When the user decides to depress the trigger 50, thecontrol switch 30 is moved to a first position in which the contact 30acompletes the circuit including the variable resistor 26, winding 5 andenergy source 25. The armature 6 is then caused to turn the shaft 10whereby the latter moves the blade 40 to the aforementioned startingposition in which the blade 40 cooperates with the fixed blade 43 todefine therewith an aperture of maximum size, i.e., the blade 40ispivoted in a counterclockwise direction so that it does not overlieany part of the objective 42. In view of such movability of the blade 40to starting position, the exposure control of the present invention canbe used with advantage in single lens reflex cameras.

As the user continues to depress the trigger 50, the control switch 30moves to a second position in which the contact 3% completes the circuitincluding the variable resistor 28, photosensitive receiver 27, winding8 and energy source 25',

the contact 30c simultaneously completes the circuit including theenergy source 25 and motor 29. A magnetic field which develops in theinstrument 3 opposes that produced by the instrument 2. Thus, thearmature 9 causes the shaft 10 to turn counter to the direction in whichthe shaft turns in response to completion of the circuit including thewinding 5. The resulting position of the blade 40 is a function of scenebrightness as determined by the photosensitive receiver 27, and theaperture size is also a function of scene brightness.

1f the potential of the energy source 25 decreases, for example, due toextended use of the photographic apparatus, the magnetic fields producedby the instruments 2 and 3 are weakened to the same extent so that suchdrop in potential does not result in improper adjustment of thediaphragm.

In order to facilitate the assembly of the moving iron instruments 2 and3, they preferably comprise cores which are assembled of severalsections. As shown in FIG. 2, the core 4 of the instrument 2 comprisestwo halves 4a, 4b which respectively comprise tonguelike sections 51, 52and 53 54. The sections 51, 53 form a pair and have complementaryinclined edge faces which abut against each other when the sections areinserted into the winding 5 from opposite ends as indicated by arrows Aand B. The same applies for the sections 52, 54. In this way, the core.4 can completely fill the interior of the winding 5 to enhance themagnetic efficiency of the instrument 2. The core 7 of the instrument 3is assembled in similar fashion.

As shown in FIG. 1, the instruments 2, 3 are angularly offset withreference to each other as considered in the direction of rotation ofthe shaft 10. It is also desirableto arrange the instruments 2, 3 insuch a way that the armature 6 tends to turn the shaft in a firstdirection when the winding 5 is energized and that the armature 9 tendsto turn the shaft 10 in the opposite direction in response toenergization ofthe winding 8.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of our contribution to the art.

We claim:

1. An exposure control for photographic apparatus, comprising diaphragmblade means; rotary carrier means operatively connected with said blademeans to move the latter between a plurality of positions including astarting position to thus furnish a range of aperture sizes; a pair ofmoving iron instruments each including core means, winding means andarmature means with both said armature means'atfixed to said carriermeans; a first electric circuit including one of said winding means; asecond electric circuit including photosensitive received means exposedto scene light and the other of said winding means; and control meansmovable between a first position to thereby complete said first circuitwhereby the corresponding armature means moves said blade means to saidstarting position, and a second position to thereby complete said secondcircuit whereby the corresponding armature means moves said blade meansto a position in which the aperture size is a function of scenebrightness.

2. An exposure control as defined in claim 1, further comprising asource of electrical energy which is connected in said first circuit inthe first position of said control means and in said second circuit inthe second position of said control means.

3. An exposure control as defined in claim 1, wherein one of saidinstruments is angularly offset with reference to the other instrumentas considered in the direction of rotation of said carrier means.

4. An exposure control as defined in claim 1, wherein said winding meansare arranged to effect angular movements of corresponding armature meansin opposite directions.

5. An exposure control as defined in claim 1, wherein each of said coremeans comprises a plurality of iriterfitted sections. 6. An exposurecontrol as defined in claim 5, wherein said sections comprise pairs oftongues having complementary inclined edge faces.

7. An exposure control as defined in claim 1, further comprising meansfor securing said core means to each other.

8. An exposure control as defined in claim 1. further comprisingdistancing means interposed between said core means.

9. An exposure control as defined in claim 1, wherein said control meanscomprises an electric switch and further comprising trigger meansoperative to move said switch between said first and second positions.

10. An exposure control as defined in claim 1, further comprising motormeans arranged to operate the film transporting mechanism of thephotographic apparatus in response to movement of said control means tosecond position.

